The satellites of the global positioning system (GPS) are of substantial assistance to surveyors. Once a mobile GPS antenna is set up on a known point on the earth's surface, and a static GPS system is placed nearby on another known point, the mobile antenna can be moved and another location of the antenna can be precisely determined, so long as the flow of signals between the satellite and the antennas has been uninterrupted during the move. The antenna can thus be moved to a point the exact location of which is required. This is normally known as kinematic GPS and employs
A complicating factor is that the antenna frequently cannot be placed precisely on the point whose position is required.
It is thus necessary in that situation to carry out the entirely separate and complicated procedure of locating the antenna relative to the known point and then to the desired point before the GPS information can be utilized.
This last requirement is a very time consuming and expensive one. This is particularly the case if one were to use a rotary wing aircraft such as a helicopter for transporting the GPS antenna. For example, if a survey is being done on an extended scale such as in the final laying out of electric power transmission lines, a large number of survey pins which will earlier have been installed by a ground survey team, must be given precise positions. The cost for the helicopter would be very substantially increased by the requirement for relating each survey pin position to the position to the antenna on the helicopter, due to the time lost for this step.
An even more basic problem exists in respect of the helicopter usage, since it is generally considered that many GPS antenna designs cannot be mounted under some types of helicopter rotors, because the spinning blades will interrupt the signal from the satellite.
Against this background, a method and apparatus has been developed which enables the GPS antenna to be mounted under the rotor of a helicopter and to be mounted in a removable manner so that the antenna itself can be precisely placed on a known and required position.